Chromium electrodeposit and method of plating



April 8, 1958 w. RAYMOND CHROMIUM ELECTRODEPOSIT AND METHOD- OF PLATING Filed June 17, 1955 2 SheetsSheet l FIG.|

am 9M IOMY (AMPS m?) CURRENT DENSITY TEMP ('C) 0 um |2M FIG. 3

FIG.2

INVENTOR LOUIS w. RAYMOND BY M a ATTORN April 8, 1958 L. w. RAYMOND ,830,

CHROMIUM ELECTRODEPOSIT AND METHOD OF PLATING Filed June 17, 1955 2 Sheets-Sheet 2 FIG. 5

INVENTOR LOUIS W. RAYMOND 62w 14k m M WJ ATTORNEY I to the Weight of the CrO ployed in accordance with the invention is higher than CHROMIUM ELECTRODEPOSIT AND METHOD OF PLATIN G .Louis W. Raymond, Fairfield, Conn., assignor to The Su- This invention relates to the electrodeposition of chromium, and more specifically, to the production of a chromium electrodeposit having a spongy structure into which an is readily absorbed and'through which oil readily permeates.

The use of chromium plating on metallic surfaces which are subjected to wear due to relative movement in order to provide superior wearing properties, has become a common expedient. Various techniques of producing hard dense chromium plating are well known and widely used. However, the problem of lubricating such a hard dense chromium surface is difficult, and devices having hard wear-resistant chromium plated surfaces, especially devices such as internal combustion engine cylinders which 'operateat high temperatures, fail simply for lack of proper lubrication. In order to avoid such failures, the surface of conventional hard, dense plating may be modified by various techniques, such as by sand blasting, selective etching, etc., in order to provide grooves or channels therein along which oil may flow to provide lubrication over'the plated area. These expedients are expensive, however, and have not proved especially satisfactory.

The present invention provides a method of producing a porous 'electrop'late having spongy structure into which oil is readily absorbed and through which oil readily permeates. A chromium plated surface in accordance with the invention is characterized by having a network of numerous interconnected veins or tunnels dispersed through the electroplate beneath the surface thereof, but communicating at frequent intervals with the surface of the electroplate. It is characteristic of such a network that it will enable oil applied to any portion of the surface of the electroplate to permeate the electroplate and spread to portions surrounding the .place at which the oil is'applied. The resulting structure is one having the hardness and wear-resistance of chromium at its surface, together with the advantage of lubrication supplied from below over the entire surface area. It has been found that this surface displays outstanding wear resistance and durability even under such severe conditions of use as prevail when itis employed on the inside of air cooled extending from 15 a. s. i. (line DE) to 75 a. s. i. (line 2-cycle internal combustion engine cylinders of highv horsepower-to-weight ratio which normally operate at high cylinder temperature.

A chromium electropl ate having the above-indicated characteristics isproduced in accordance with the invention by electrodeposition from an aqueous electrolyte containing from 150 to 600 grains per liter of CrO and a catalyst selected from the group consisting of sulfate ions and fluoride ions in an amount in a range from The current density emcan be used in producing hard, dense chromium electroplates, and is, in-anyev'ent, greater than 12 amperes per square: inch of cathode surface. The temperature of the electrolyte in relation to'the cathode current density employed also'iscritical, and must be maintained at a value I '55" '0. (line EF).

2,830,015 Patented Apr. 8, 1958 range from 15 to amperes per square inch of cathode surface.

It is common practice to form hard, dense chromium electroplates at relatively low current densities and at relatively low electrolyte temperatures (e. g., at about 35 C. and at 5 to 10 amperes per square inch of cathode surface, hereinafter abbreviated a. s. i.). Proposals have also been made to produce hard, dense chromium electroplates at higher temperatures and current densities than are generally used (as described, for example, in U. S. patent to Wick No. 2,392,871). These proposals have sometimes involved the use of current densities as high as the minimum used in making porous electroplates according to this invention, but invariably such high current. densities have required the use of a considerably higher electrolyte temperature than can be tolerated in order to produce the porous electroplate provided by this invention.

tion of a metallic surface which has been electroplated in accordance with the present invention, showing the spongy porous nature of the electrodeposit;

, Fig. 3 is a much enlarged plan view of a portion of the'surface shown in Fig. 2;

Fig. 4 is a photomicrograph of a section taken through a portion of an electroplated surface produced in accordance with the present invention said section being enlarged 300 times, and

Fig. 5 is a photomicrograph showing a portion of the surfaceof the electroplate shown in section in Fig. 4, but in this instance enlarged 75 times.

Referring to Fig. 1, a graph showing. the area of operation of the method of the present invention is illustrated. In this graph, :the ordinate is temperature in degrees centigrade and the abscissa is current density, in amperes persquare foot. As shown, there is a minimum of current density below which a satisfactory porous electrocannot be had varies with current density and is indicated by line BC. Within the bounds ABC is a preferred region of operation wherein superior results have been obtained. This preferred region is a rectangular area PG) The minimum temperature of this preferred region is 30 C. (line DG) and the maximum temperature is The region satisfactory for electroplating, in accordance with the present invention, has beenexperimentally determined by making a great many samples employing various combinations of temperature and current density, and it has been found that, as these limiting points are approached, the porosity of the electro plate decreases materially to a point where it is unsatisfactory. Some porosity may be obtained beyond these limits but the veins are either too sparse or not sufliciently interconnected to be effective. Accordingly,

as a practical matter, the process must be kept within the limits of lines ABC for a satisfactorily porous product. The line XY has been drawn on this graph to indicate the lower limit of electrolyte temperatures at which the V 3 process of Wick will produce satisfactory results which, in his case, is a hard, dense, non-porous chromium plate.

Prior to plating a metallic surface in accordance with the present invention, it is desirable to clean and degrease the base metal in the conventional manner. A zincate dip is also often desirable prior to plating to improve the adhesion of the plating to the base metal. Thereafter, plating may be done in accordance with the method of the present invention. The plating bath may have from 150 to 600 grams per liter of chromic acid, but a range of 200 to 400 grams per liter is'preferred. The sulfate or fluoride ion catalyst furnished, for 1 example, by

H 50 is added in amounts varying from 2 to 10 grams per liter and preferably from 2 to 5 grams per liter. The ratio of catalyst to Cr will be greater than 1:150 and usually in the neighborhood of 1:100; Trivalent. chromium may be present without harm, as in ordinary chromium plating operations, in amounts up to 8 grams per liter.

In the actual plating operation, the bath adjacent the surface to be plated must be maintained within the bounds of current density and temperature, defined in the graph of Fig. l by the lines AB and BC.

Figs. 2 and 3 show what might be termed a highly magnified idealized view of the form in which the electrodeposit of the present invention occurs. The base metal 10 may be of any type satisfactory for plating with chromium depending on the particular application to which the electroplated structure is to be used. The electrodeposit 11, as seen in Figs. 2 and 3, is filled with a network of small interconnected veins 12 beneath the surface, and these veins as may be seen in Fig. 3, communicate with the surface at frequent intervals; It is characteristic of the structure of thepresent invention that the many small subsurface veins will cause a drop of oil placed on the surface of the electroplate 11 to be drawn into the holes by capillary attraction. Since the holes are interconnected, oil placed at one point on the surface, will tend to pass through the holes in all directions and return to the surface at points removed from the initial point of application so that effectively the oil tends to spread out evenly inall directions.

Referring to the photomicrographs, the profusion of subsurface veins is immediately apparent in Fig. 4. It is obvious from the much less magnified photomicrograph of the extend to the surface of the metal relatively infrequently when compared with the length of the subsurface veins.

However, one needs only to'recall that Fig. is magnifiied 75 times torealize that there are a great number of holes in the surface so that adequate lubrication is assured. Accordingly, the plated surface shown in these photomicrographs is satisfactory for'such uses as the cylinder liner of internal combustion engines and as the bearing surface on the tracks or ways of machine tools,

and other heavy machinery.

The sample from which the photomicrographs of Figs...

4 and 5 were taken is typical of the product of the present invention. This sample was plated in an electrolyte containing 347 grams per liter of chromic oxide, 3.6 grams per liter of sulfate. It was found that there were 7.3 grams per liter of trivalent chromium in the electrolyte. The bath temperature was 43 C. and the current density 4320 amperes per square foot.

Samples made in various other portions of the preferred region differed slightly in appearance but all had a profusion of interconnected subsurface veins. Outside of the preferred region but within the permissible range of temperature and current density somewhat fewer veins per unit area of ,plated surface are usually obtained, but satisfactory electrodeposit from the standpoint of their spongy oil absorbing qualities are still obtained.

A particularly advantageous use of a porous electroplate, according to the invention, is as a wear-resistant lining on the inside of an internal combustionengine cylinder. There is a trend toward increasing the horsepower-to-weight ratio of internal combustion engines used to power portable tools such as chain saws, used by woodsmen. Such increase can be achieved only at the expense of increased cylinder operating temperatures. The higher cylinder temperatures in turn greatly increase the difficulty of providing a lubricating film on the inside surface of the cylinder, and they also necessitate maximum efficiency of heat transfer through the cylinder wall. The new electroplate provided by this invention admirably meets both of these difliculties. The ease withwhich oil permeates through its subsurface veins assures that the surface of the electroplate will be welllubricated; and its thinness and the tightness with which it binds to the cylinder bloclcmetal (usually aluminum) assures that it will impose a minimum restriction on heat transfer through the cylinder block to the heat dissipating devices of the engine.

Another advantageous use of the new porous chromium electroplate is as a wear resistant film on machine tool ways, when a high degree of wear resistance together with excellence of lubrication of the way surfaces are required.

I claim:

1. The method of producing a porous chromium electroplate having a spongy structure into which oil is readily absorbed and through which oil readily permeates, which comprises electrolytically depositing chromium on a work piece cathode from-an aqueous electrolyte con-' taining from 150 to 600 grams per liter of CrO and a catalyst selected from the group consisting of sulfate ions and fluoride ions in an amount in the range from to $4 the weight of the CrO the current density being maintained at a value exceeding 12 amperes per square inch of cathode surface and the temperature of the electrolyte being substantially below, and sufliciently less than the value indicated by the line BC on Fig. 1 of the drawingsfor the particular current density employed to produce said porous, spongy chromium electroplate.

2. The method of producing a porous chromium electroplate having a spongy structure into which oil is readily absorbed and through which oil readily permeates,

surface that, by comparisom these Veins taining 200 to 400 selected from the group consisting of sulfate ions and which comprises electrolyticallydepositing chromium on a work piece cathode from an aqueous electrolyte congrams per liter of CrO and the catalyst fluoride ions in an amount in the. range from A to the weight of the C10 the current density being maintained at a value exceeding 12 amperes per square inch of cathode surfaceand the temperature of the electrolyte being substantially below, and sufiiciently less than the value indicated bythe line BC on Fig. l of the drawings for the particular current density employed to produce said porous, spongy chromium electroplate.

3. The method of producing a porous chromium elec- ;'troplate'having a spongy structure into which oilis readily absorbed and through 'which'oil readily permeates,

V which comprises electrolytically depositing chromium on a work piece cathode from an aqueous electrolyte containing from 150 to 600 grams per liter of CrO and a catalyst selected from the group consisting of sulfate ions and fluoride ions in an amount approximately A of the weight of CrO the current density being maintained at a value exceeding 12 amperesj per square inch of cathode surface and the temperatureof the electrolyte being substantially below, and sufficien tly less than the value indicated by the line BC on Fig. 1 of the drawings for the particularcurrent density employed to produce said porous, spongy chromium electroplate.

4. The method of producing a porous chromium eleci troplate having a spongy structure into which oil is readily absorbed and through which oil readily permeates, which comprises electrolytically depositing chromium on a work piece from an aqueous electrolyte containing from 150 to 600 grams per liter of Cr0 'a'ndf a catalyst selected from the group consisting of sulfate ions and fluoride ions in an amount in a range from to ,4, the Weight of the CrO the temperature of the electrolyte being in the range from 30 C. to 55 C. and the cathode current density being in the range from to 75 amperes per square inch.

5. The method of producing a porous chromium electroplate having a spongy structure into which oil is readily absorbed and through which oil readily permeates, which comprises electrolytically depositing chromium on a Work piece from an aqueous electrolyte containing from 200 to 400 grams per liter of CrO and a catalyst selected from the group consisting of sulfate ions and fluoride ions in an amount approximately ,4 the weight of CrO and in any event less than 3.0 grams per liter of electrolyte solution, the temperature of the electrolyte being in the range from C. to C. and the cathode current density being in the range from 15 to amperes per square inch.

References Cited in the file of this patent UNITED STATES PATENTS 2,392,871 Wick Jan. 15, 1946 2,412,698 Van Der Horst Dec. 17, 1946 2,430,750 Webersinn et al Nov. 11, 1947 2,450,296 Passalacqua Sept. 28, 1948 10 2,497,591 Dubpernell Feb. 14, 1950 2,534,408 Bramberry Dec. 19, 1950 OTHER REFERENCES Dubpernell: Transactions Electrochemical Society,

15 special issue, Modern electroplating, 1942, pp. 117-126. 

1. THE METHOD OF PRODUCING A POROUS CHROMIUM ELECTROPLATE HAVING A SPONGY STRUCTURE INTO WHICH OIL IS READILY ABSORBED AND THROUGH WHICH OIL READILY PREMEATES WHICH COMPRISES ELECTROLYTICALLY DEPOSITING CHROMIUM ON A WORK PIECE CATHODE FROM AN AQUEOUS ELECTROLYTE CONTAINING FROM 150 TO 600 GRAMS PER LITER OF CRO3 AND A CATALYST SELECTED FROM THE GROUP CONSISTING OF SULFATE IONS AND FLUORIDE IONS IN AN AMOUNT IN THE RANGE FROM 1/150 TO 1/80 THE WEIGHT OF THE CRO3, THE CURRENT DENSITY BEING MAINTAINED AT A VALUE EXCEEDING 12 AMPERERS PER SQUARE INCH OF CATHODE SURFACE AND THE TEMPERATURE OF THE ELECTROLYTE BEING SUBSTANTIALLY BELOW, AND SUFFICIENTLY LESS THAN THE VALUE INDICATED BY THE LINE BC ON FIG. 1 OF THE DRAWINGS FOR THE PARTICULAR CURRENT DENSITY EMPLOYED TO PRODUCE SAID POROUS, SPONGY CHROMIUM ELECTROPLATE. 